1. Field of the Invention
The invention relates to a developing device for use with an image forming apparatus that forms images by electrophotographic processes. Toner is supplied from a toner introduction port after being stirred in a toner cartridge by the rotation of an agitator that is attached to a rotary shaft in the toner cartridge which forms a toner reservoir. The invention also relates to a toner cartridge for use with the developing device. More particularly, the invention relates to a developing device for use with an image forming apparatus, which controls the toner in the toner cartridge properly with respect to the diffusion of toner.
2. Description of the Related Art
Various types of developing devices have been proposed for use with electrophotographic image forming apparatuses such as laser printers. Most of these developing devices are formed so that they can be mounted on laser printers as a module device. In addition, they are provided with a replaceable toner cartridge which is used as a toner reservoir.
An example of such a developing device will be explained with reference to FIG. 17. FIG. 17 shows an essential portion of a typical related art developing device.
As shown in FIG. 17, the developing device is provided with a toner cartridge 100 that contains toner and has a toner introduction port 101. An agitator 103 is provided in the toner cartridge 100 that stirs toner. A toner introduction port F0 is formed at a frame F of a process cartridge holding the toner cartridge 100, corresponding to the toner introduction port 101 of the toner cartridge 100. A toner supply roller 104 is rotatably disposed in the lower portion of a developing chamber 102 that is defined by an upper frame F1 and a lower frame F2. A developing roller 105 is adjacent to the toner supply roller 104. The supply roller 104 supplies the toner to the developing roller 105 via port 101 and port F0.
In addition, a blade 107 is fixed to the inner wall of the upper frame F1 via a fixing member 106 at a position above the developing roller 105. The blade 107 limits the thickness of the toner layer formed on the surface of the developing roller 105. Furthermore, the developing roller 105 is disposed so as to contact a photosensitive drum 108. An electrostatic latent image is formed on the surface of the photosensitive drum 108 by a light exposure device (not illustrated) that scans a laser beam according to image data. The developing roller 105 develops images with toner supplied to the latent image formed on the surface of the photosensitive drum 108. The image developed on the photosensitive drum 108 with the toner is then transferred onto a sheet supplied from a sheet feeder (not illustrated).
In the toner cartridge 100 for use with a developing device as mentioned above, the toner in the cartridge 100 is slowly consumed, so that a residual toner level is detected. When the level is low, the toner cartridge 100 must be replaced. If the toner cartridge which is used as a toner reservoir is formed integrally with the process cartridge and cannot be removed from the process cartridge, the process cartridge must also be replaced with the toner cartridge. In order to detect the residual toner level, an optical sensor is generally disposed to detect toner existing at a detecting point in the toner cartridge 100.
When an ample supply of toner remains in the toner cartridge 100, the toner blocks the sensor beam at the detecting point. The toner, however, scatters when the agitator is rotated. The sensor beam thus passes the detecting point without detecting any toner, even though an ample amount of toner still remains. This results in a false detection (that the toner level is low) in some cases.